1. Field of the Invention
The invention relates in general to a current source, and more particularly to a current source having a voltage-current coefficient, which is defined by a difference of an output current per a supply voltage, with different values while the output current is kept within a fixed current range.
2. Description of the Related Art
In virtually all circuitry using integrated analog circuits, reference voltages or reference currents are required. Generally, reference currents are provided by current source, which is supposed to be constant under all operating conditions and should either have no temperature drift or a defined temperature drift coefficient. In some application, user has the inclination to have a current source a defined voltage-current coefficient, which is similarly defined as the temperature drift coefficient, with tunable delta current per delta voltage.
It is obvious that the operation of tuning the voltage-current coefficient can be achieved by tuning the equivalent resistance of the current source. However, the approach of directly tuning the equivalent resistance of the current source will also result in variation of DC current level, which is unwanted by the circuit user. Thus, how to provide a current source with tunable voltage-current coefficient while capable of keeping the DC current level within a fixed current range is a prominent object for the industries.